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Computer simulation and investigation of underwater two-part and multi tow systems

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Ranmuthugala, Susantha D.(Susantha Devapriya) 2000 , 'Computer simulation and investigation of underwater two-part and multi tow systems', PhD thesis, University of Tasmania.

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Abstract

To maximise effectiveness, towed underwater sonar bodies generally require
perturbations from the steady state motion to be minimised. The instantaneous
position of the towed body is influenced by the unsteady, wave-induced motion of the
surface vessel, transmitted via the tow cable. This can render the trajectory of the
underwater body beyond acceptable limits for sonar operations.
In an effort to decouple this motion, a two-part tow configuration has been employed.
This thesis describes a three-dimensional dynamic computer model developed to
investigate two-part tows by modelling the individual cabl~s separately and coupling
them dynamically. This approach also enables the modelling of series and parallel
multiple tow configurations. The cable system, modelled using a three degree-offreedom
finite difference approach, is then coupled to the ·six degree-of-freedom
underwater towed bodies at the appropriate locations of the cable system. The
modelling of the cable as a continuous medium and the derivation of the stress wave
speeds are also presented, followed by the validity and.effects of representing it as a
discretised model.
The solution to the dynamic equations describing the motion of the discretised tow
configuration is carried out using an implicit multi-step numerical technique, subject
to specific boundary conditions. This allows the values to be improved through an
iterative procedure, until sufficient convergence is achieved.
An introduction into the use of such numerical techniques in engineering and an
analysis of the numerical procedure used in the solution are also presented. The
requirements for accuracy and numerical stability of the integration technique are
investigated and a guide to the time interval for the time ·stepping algorithm is
deduced.
The computer model is successfully validated using experimental results from scaled
model tests in a circulating water channel. These results together with those obtained
from full scale sonar trials utilising small coastal craft are used to further investigate
the behaviour of the two-part tow configuration to varying parameters. The
experimental results and the computer model enables the user to identify the optimum tow configuration for the prevailing conditions.
The thesis also presents a detailed review of the various methods available to
investigate underwater cables and vehicles, together with prediction methods for their
hydrodynamic coefficients. The latter coefficients for the scaled models used in the
project are obtained via experimental procedures.
Although a number of investigations have been carried out dealing with aspects of
underwater towing operations, the strength of this investigation lies in that it combines
these aspects, i.e._ mathematical modelling, computer simulation, prediction of the
hydrodynamic coefficients, scaled model experiments, full scale trials, and the
analysis of the numerical technique, into one study.

Item Type: Thesis - PhD
Authors/Creators:Ranmuthugala, Susantha D.(Susantha Devapriya)
Keywords: Ultrasonic equipment, Sonar
Copyright Holders: The Author
Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

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